Certain control devices for melting vessels, such as steel melting vessels, consist mainly of a lance along with a probe which has a sensor and sampling section at the lower end of the probe held on by means of a pasteboard or cardboard tube which is attached to the lance by means of a connecting tube. The uppermost annular face of the pasteboard or cardboard tube fits against a juncture surface of the lance. Within the pasteboard or cardboard tube there is an electrical connector with contacts which are connected to a mating piece on the connecting tube when the probe is put on.
During the operation of such a device, especially in steel convertors, deposits form on the lance and on the juncture surface of the pasteboard or cardboard tube. Both slag and steel deposits are involved, and hereinafter both types are generically referred to as deposits. These deposits originate because of splashes resulting from the bubbling of gases in the converter. The lower surface of the lance can be additionally fouled by deposits which occur because of initially-liquid deposits which flow downward from the casing of the measuring lance and which then solidify to form a collar of deposits
The result of such deposits at the juncture is that after a number of insertions of the lance into the converter for the taking of measurements, because of the buildup of deposits associated therewith, it becomes difficult to attach new probes. The length tolerance in the coupling is exceeded, with the result that reliable electrical contacts can no longer be achieved, rather, interruptions and short circuits occur. Moreover, deposits can form on the connecting tube itself, especially at its opening into the lance, which leads to additional mechanical difficulties. The extra thermal protection offered by the pasteboard tube to the connecting tube can also be partly lost, resulting in damage to the connecting tube.
To avoid these operational difficulties in the apparatus caused by such deposit formation, these deposits must be removed on a routine maintenance basis as well as when special need arises. This work has to be carried out in a dangerous environment with exposure to dust and heat, and it increases the operating expense of the plant.
To avoid these collar-like deposits, in accordance with European Patent Application No. 0143498, the use of elastic rings between the lance and the probe has been proposed. However, the use of such rings in actual practice entails serious difficulties.